1. Field of the Invention
This invention relates to a process for the oxidation of propylene to form allyl acetate, a specialty chemical useful as a precursor to allyl alcohol and other articles of commerce. More particularly, this process is directed to the improvement of oxidizing propylene in one step in the presence of acetic acid to form allyl acetate at high selectivities and yields under moderate reaction conditions in the liquid phase by the use of a novel olefin-activated palladium catalyst.
2. Description of the Prior Art
The literature reports that palladium catalysts of several different types promote the oxidation of propylene to allyl acetate in the presence of acetic acid. One type of catalyst is a silica-supported palladium catalyst (U.S. Pat. No. 3,925,452) which requires elevated temperature (&gt;140.degree. C.) and produces carbon dioxide as the major by-product. A stoichiometric oxidant-PdCl.sub.2, together with large amounts of sodium acetate (J.A.C.S., 98,6913 (1976)) operates in the liquid phase at low temperature (25.degree.-100.degree. C.) but produces 2-acetoxypropene as a significant by-product. Typical soluble Palladium and copper chloride and acetate catalyst systems give very poor allyl acetate selectivity when used in acetic acid in the presence of acetate ion (Clark, Hayden and Smith, Discuss. Faraday Soc., 46, 98 (1968)). Another type of catalyst, palladium trifluoroacetate, operates under mild conditions in the liquid phase to give allyl acetate as the predominant product (French Patent No. 79-05874 (1980)) but catalyst recovery for re-use is difficult. Thus, allyl acetate has been prepared by heterogeneous catalysts in the vapor phase at high temperature or by a soluble catalyst in the liquid phase at low temperature. In the former case reaction selectivity is a problem and in the latter case both selectivity and catalyst recovery are major difficulties.
In addition, Hinnenkamp, U.S. Pat. No. 4,435,598; Scharfe, U.S. Pat. No. 3,970,713; Onoda, U.S. Pat. No. 4,016,200; and Slesser, Brit. Pat. No. 1,251,831 teach conventional methods for oxidizing olefins in the presence of palladium catalysts, wherein said catalysts are prepared by reducing palladium salts with various reducing agents including olefins under routine reduction conditions. Scharfe, whose catalyst is impregnated with potassium acetate for use in oxidizing propylene to allyl acetate, additionally makes the obvious point that it is commercially advantageous, although not essential, to carry out the reduction before introducing the volumes of oxygen needed for oxidation. Nowhere, however, is there any recognition of preparing the catalyst in the substantial absence of oxygen, or the benefits to be derived therefrom. Similarly, Hartley, "The Chemistry of Platinum and Palladium," Wiley and Sons, pp. 386-390 and 412-417 (1973) discloses a method for making a palladium chloride catalyst complexed with ethylene for use in the acetylation of olefins to vinylic acetates. However, none of these prior art teachings disclose the use of a unique olefin-activated palladium metal catalyst as defined herein to prepare allyl acetate from propylene.
Finally, Holzrichter, U.S. Pat. No. 3,275,680, teaches oxidizing propylene to allyl acetate in the presence of acetic acid and a palladium catalyst. However, a totally different catalyst system than is claimed hereinbelow, prepared by the reduction of palladium salts with hydrazine, is taught. Moreover, the ultimate conversion of propylene, and yields per pass, are relatively low.
Therefore, it is an object of this invention to provide an improved process for converting propylene to allyl acetate in one step at high yields and selectivities, as contrasted with reported prior art methods, utilizing an easily recovered heterogeneous catalyst in the liquid phase under mild conditions.
Other objects of this invention will be evident from the description and examples set forth hereinbelow.